The report, which analyzes survey data collected last year, showed an uptick in the percentage of marijuana users. In fact, the percentage of Americans who admitted to regular illicit drug use increased for most age groups from 2009 (see graph below).

According to USA Today, marijuana is also the most widely used illicit drug, with 6.9 percent of the population admitting to regular use. The reason for its increased prevalence may also be attributed to the increasing number of states that have approved its consumption for medical purposes.

Meth, on the other hand, has taken a sharp downturn in usage.

From USA Today:

Meanwhile, methamphetamine use, which raced across the USA for a decade, has declined sharply. The number of past-month users declined from 731,000 in 2006 to 353,000 in 2010.